The prior art discloses a number of transparent plastic eye shields, sunglasses, goggles and spectacles with a one piece front hinged to narrow as well as wide flangeless temple bars and side guards or shield.
However, the primary purposes thereof is to protect the eyes from dust, wind, rain, sunlight and glare and in some cases are merely for ornamental or fashionable purposes. Hence, they do not provide adequate protection against the more dangerous industrial hazards and impact of flying objects or particles associated with construction or manufacturing processes and accidents.
Further, the prior art one piece front face piece members do not have a single spherically curved eye shield portion of high optical quality and hence has a tendency to distort the image viewed therethrough at various angles.
Although some front members have a flange which engages the forehead, the temple bars hinged thereto do not have curved protective flanges continuing around the temporal area from curved ends of the front member.
The plano spectacles of the invention are also provided with integrally molded plastic hinges. They differ from prior art hinges in that the temple bar pivot pins and the pivot pin receiving apertures on the front member or face piece have an elongated or oblong, interlocking and interfitting shape with outwardly extending mating tapered surfaces on one side thereof. Thus, they are interlocked and, a slight resistance to unintentional relative pivoted movement is provided to maintain them in the wearing position.
Further, the one-piece protective front of the applicants spectacles has a number of advantages with respect to both protection and optical characteristics.
Mechanically it offers the strength of tough polycarbonate optics and frame fronts since the two are combined. It eliminates the danger of lens displacement and provides excellent protection above and to the sides of the optical area.
Safety spectacles without side shields offer limited protection. Conventional side shields are awkward and restrict vision. The applicants spectacles offers a very wide visual field; the same continuous field as a 66 mm lens would offer--greater than any conventional safety spectacle and does this with no nasal interruption. The full field of view is a safety factor in itself.
Also, the one-piece front design offers visual advantages in acuity and comfort unlikely to be provided by a spectacle system consisting of a frame with two independent lenses. These advantages stem from the inherent control of the balance of optical effects between the two eyes. This is because with respect in small amounts of inherent power, prism, and astigmatic errors, the principal concern is imbalance between the eyes.
Power and astigmatic imbalance frustrate accommodation, lower acuity, and can cause space perception problems.